A working vehicle such as a wheel loader includes an exhaust aftertreatment device (e.g., a diesel oxidant catalyst (DOC) and a selective catalytic reduction (SCR)) provided in an exhaust passage of an engine, the exhaust aftertreatment device being configured to burn particulate matters (PM) existing in an exhaust gas and purify nitrogen oxides (NOx) existing in the exhaust gas (see, for instance, Patent Literature 1).
In order to burn PM and purify NOx, it is required to increase a temperature of the exhaust gas. Accordingly, an exhaust throttle valve is provided in the exhaust passage upstream of the exhaust aftertreatment device, and the temperature of the exhaust gas is controlled by controlling an open degree of the exhaust throttle valve, so that the exhaust aftertreatment device is functionally optimized.
However, a frequent control of the open degree by the exhaust throttle valve causes abrasion on sliding surfaces between a bearing member and a valve body in the exhaust throttle valve. When the abrasion progresses, the exhaust throttle valve interferes with a housing to shorten a working lifetime.
Accordingly, Patent Literature 2 discloses a technique of forming the bearing member using a heat-resistant alloy (e.g., Inconel (trade mark)) formed of a sintered metal.